Hello there.
I own the 990, have an older MC12B which has been upgraded to V.5, and use the Lexicon MC12B-HD/EQ at an install I did at my job site. Gonk and Sanjay offer excellent points and I don't have much substance to add except, get what you think is appropriate for your level of financial resources and needs. To answer your question of comparison, I have compared the 990 and the MC12B at home extensively and usually come away impressed by the quality of sound of the 990 which is 1/10th(!) the price of the MC12B. Ok, sure there is a smidgen more air and depth in 2 channel music but for movie watching, I don't hear a difference that is qualitatively any better. (Interesting to note, if I add my external DAC and the X-Ray V3, the field is pretty level for 1/9th the price of the Lexi. So bottom line: I use the Outlaw because I love knowing I am getting extreme value and quality.) If you are looking for HDMI and are looking forward to parting with your hard earned cash, go with components that are specifically designed to suit your needs since you already have a great pre/pro, buy a nice scaler instead. I use both the Pixelmagic Crystalio II ($10k+) and the DVDO iScan VP50 ($3k) and think both are very good. At the office install, I actually bypass the HD in the MC12B and go straight to the Crystalio because it is a far better scaler than what is built into the MC12. (I use a Projection Design 1080p Projector via HDMI.) The one aspect that I do love about the Lexi is that it has very deep levels of controls. You can tweak the heck out of virtually everything type of adjustment you can think of. I’d love to infinitely adjust every surround processing choice for my specific output on the Outlaw but it isn’t critical to my enjoyment of music and movies. But hey, if you have $13k burning a hole in your pocket then by all means get the MC12B-HD/EQ and reap the benefits of a quality Swiss army of processers at, well, not Swiss army prices.